WASHINGTON — Chief Justice William Rehnquist, who served on a Supreme Court that spanned Watergate, impeachment and the presidential election of 2000, died last night at his home in Arlington, Va., following complications of thyroid cancer.

A statement from a court spokeswoman said the 80-year-old justice was surrounded by his three children when he died shortly before 11 p.m. Eastern time.

"The chief justice battled thyroid cancer since being diagnosed last October and continued to perform his duties on the court until a precipitous decline in his health the last couple of days," she said.

His death comes almost on the eve of the nomination hearings for John Roberts Jr., who was named by President Bush to replace Justice Sandra Day O'Connor, and it throws the process into unexpected turbulence just a month before the start of the new court term.

Rehnquist, taciturn in public and engaging in private, served on a court that had been intact longer than any nine-member panel in history. Nominated by President Richard Nixon, Rehnquist helped define conservatism through the court as the nation moved to the right in the last generation.

Along with Justices Antonin Scalia and Clarence Thomas, Rehnquist helped to shape the boundaries of issues in American life from the death penalty to abortion to the outcome of a presidential election.

"President Bush and Mrs. Bush are saddened by the news," said White House counselor Dan Bartlett. "It's a tremendous loss for our nation." The president was expected to make a personal statement about Rehnquist today.

Rehnquist was appointed to the Supreme Court as an associate justice in 1971 by Nixon and took his seat on Jan. 7, 1972. He was elevated to chief justice by President Ronald Reagan in 1986.

His death ends a remarkable Supreme Court career during which Rehnquist oversaw the court's conservative shift, presided over an impeachment trial and helped decide a presidential election.

The death gives President Bush his second court opening within a few months and sets up what's expected to be an even more bruising Senate confirmation battle than that of John Roberts Jr.

Rehnquist presided over President Bill Clinton's impeachment trial in 1999, helped settle the 2000 presidential election in Bush's favor and fashioned decisions over the years that diluted the powers of the federal government while strengthening those of the states.

The chief justice passed up a chance to step down over the summer, which would have given the Senate a chance to confirm his successor while the court was out of session, and instead Justice Sandra Day O'Connor announced her retirement to spend time with her ill husband. Bush chose Roberts, a former Rehnquist clerk and friend, to replace O'Connor.

The president could elevate to chief justice one of the court's conservatives, such as Antonin Scalia or Clarence Thomas, but it's more likely he will choose someone from outside the court.

Possible replacements include Attorney General Alberto Gonzales and federal appeals judges J. Michael Luttig, Edith Clement, Samuel Alito Jr., Michael McConnell, Emilio Garza and James Harvie Wilkinson III.

Rehnquist announced last October that he had thyroid cancer. He had a trachea tube inserted to help him breathe and underwent radiation and chemotherapy treatments. Details of the chief justice's illness and his plans had been tightly guarded. He looked frail at Bush's inauguration in January and missed five months of court sessions before returning to the bench.

On the court's final day of last term, June 27, Rehnquist appeared gaunt and had difficulty as he announced the last decision of the term — an opinion he wrote upholding a Ten Commandments display in Texas. His breathing was labored, and he kept the explanation short.

He had no public appearances over the summer, although he was filmed by television crews in July as he left the hospital following two nights for treatment of a fever.

Rehnquist's death came after serving 33 years on the court, 19 of them as chief justice.